The invention relates to a screw-nut assembly including an integrated, immediately effective securing arrangement for preventing unintentional loosening of a screwed connection formed thereby, the assembly comprising a first screw connection body and an associated second screw connection body. The expression “screw-nut assembly” as used in this application is to be understood as one comprising any type of screwed connection wherein there is a mating of external and internal threads.
Locking washers are usually used for securing screw-nut connections, such washers being arranged below the nut when the screw or the nut is applied so that the effects produced by spring tension or frictional force prevent the assembly from loosening itself.
Furthermore, it is known to secure nuts by using additional positive-locking means which co-operate with the screw or another part fixed to the screw such as split pins, securing wires or the like for example. Here too, an additional element for securing the screw must be attached when mounting the screw and this element must be removed before it can be undone. Thus, these aforementioned techniques do not incorporate an integrated securing arrangement for the screw-nut connection.
Moreover, self-locking nuts and screws are known which incorporate an integrated securing element with the aid of which an immediate securing effect for preventing the assembly from loosening is obtained by virtue of the frictional engagement at the flanks of the threads. However, the disadvantage here is that the increased, loosening-inhibiting friction is also effective during the tightening process so that screw-operating tools must be used even during the pre-assembly process.
In the case of securing arrangements for singular screw-nut connections which enable the screw-nut connection to be rotated until the onset of the securing effect, the biasing force within the screw-nut connection can, in dependence on the type of screw securing arrangement, be reduced to zero until the screw securing arrangement becomes effective. Because there is then a lack of biasing force, the parts being screwed together by means of the screw-nut connection can undergo relative movements when forces are applied to these parts. For their part, these relative movements exert large forces on the screw-nut connection which can lead to the destruction of the screw-nut connection or that of its securing device. Such kinds of destruction have already occurred in the case of the wheels having a central quick-release mechanism which are used in motor sports for example.
In the automobile field, it has been known for a long time that unintentional opening of the wheel nuts, and especially the release of a so-called central quick-release mechanism, can be prevented by means of mechanically effective integrated aids. Thus, for example, DE 249 305 discloses a central quick-release mechanism for a vehicle wheel wherein a wheel nut is provided with an internally toothed ring-shaped collar at the front end thereof as seen in the direction of tightening. These internal teeth co-operate with external teeth on a bushing which is arranged on the wheel hub and is non-rotatable relative to the wheel hub while being axially displaceable against spring action. When screwing the wheel nut onto the wheel hub by means of a special tool, axially parallel pins that are arranged in a displaceable manner in the nut are pressed forwardly in the direction of tightening by the tool and keep the bushing spaced from the nut. It is only when the tool is removed that the bushing is pressed towards the nut by spring action, whereupon the external teeth of the bushing engage in the internal teeth in the collar of the nut and this thus prevents further rotation in both directions of rotation. However, in this securing arrangement, it is necessary for the nut to be located at the correct angle relative to the bushing in order to enable the teeth to engage with one another. Consequently, this nut securing arrangement is not a step-less arrangement. If the nut has to be tightened using a given torque, then it is generally necessary for the nut to be rotated backwards or forwards through some angular degrees after it has been tightened correctly in order to enable the parts to latch together and thus secure the nut.
A step-less nut securing arrangement for a central quick-release arrangement for a vehicle wheel is known from DE 263 371. Here, the nut is provided with a brake lever in the region where the outer peripheral surface thereof comes into contact with the inner periphery of the wheel rim boring, the brake lever being pressed against the inner periphery of the rim boring by the action of a spring. The lever is mounted slightly eccentrically so that it becomes clamped to the inner peripheral surface when the nut is rotated in the opening direction. For the purposes of loosening the nut, the lever must be pivoted by an additional tool against the action of the spring in order to overcome the clamping effect. This device is complex and expensive to manufacture and is unwieldy in practice, and the reliable manipulation thereof is severely restricted.